The present invention relates to tracking systems. More particularly, the invention comprises a system and method for tracking a plurality of persons or objects with a plurality of spotlights.
In the entertainment industry, a very frequent requirement is for one or more spotlights to track one or more persons or objects moving about a stage. In addition, the characteristics of the spotlights (focus, color, intensity, shape, etc.) must be changed quite frequently during the course of a performance of a show. In the past, the foregoing functions were performed by skilled workers. That practice required considerable time for rehearsal of the lighting workers, was prone to human error, and involved significant salary expense. These problems are compounded for a show that is "on the road." A show's management has two choices with regard to lighting workers: (1) hire workers to travel with the show, which involves considerable salary, travel, lodging, and meal expense; or (2) hire local workers, which requires that new workers be rehearsed in each location and results in a generally high rate of error.
Relatively recently, lighting control consoles have become quite common. Such consoles allow centralized control over the characteristics of a show's spotlights. However, prior to the present invention, no accurate, cost-effective system for aiming the spotlights at persons or objects moving on a stage had been developed.
U.S. Pat. No. 4,067,015 (Mogavero et al.) discloses a system in which each individual or object to be tracked is provided with a radio frequency or ultrasonic transmitter. An array of receivers receives the transmitter's signal. An appropriately-programmed computer determines the location of the transmitter using the phase difference between the signals received by different receivers. A servomechanism then acts to direct the beam of a spotlight at the person or object to which the transmitter is attached.
In U.S. Pat. No. 4,264,928 (Schober), adjacent microphones receive the sound waves from a person speaking. The time difference between the arrival of the sound waves at the microphones is used to position a beam of light on the speaker.
U.S. Pat. No. 4,905,315 (Solari et al.) describes a system in which a number of sensors on a rotatable platform are disposed at angularly spaced intervals on a vertical plane and on a horizontal plane. A control signal radiated by an infrared light transmitter is attached to a moving object. The beam width of the transmitter's signal is such that it is normally received at only one or two of the sensors. A control system acts to rotate the platform horizontally and vertically so that the transmitter's signal is received by detectors immediately adjacent to the line formed by the intersection of the horizontal and vertical planes, thereby aiming a device mounted on the platform at the transmitter.
U.S. Pat. No. 4,980,871 (Sieber et al.) discloses an ultrasonic tracking system in which an ultrasonic transmitter is attached to the person or object to be tracked. The transmitter periodically transmits brief ultrasonic bursts. An array of three microphones is attached to a drive unit capable of panning and tilting. A control system compares the times of arrival of signals at the microphones, then pans and tilts the drive unit until the signals arrive at the microphones simultaneously, which occurs only when an aiming line of the drive unit is pointed directly at the transmitter.
U.S. Pat. No. 5,150,310 (Greenspun et al.) discloses a method and apparatus for position detection in which a transmitter attached to a person or object to be tracked periodically emits a burst of pulsed energy. The spatial position of the transmitter is determined by calculations based on the differences in the arrival times of the transmitter's signal at a plurality of receivers that are disposed at known locations.
U.S. Pat. No. 5,179,421 (Parker et al.) discloses a system in which an infrared transmitter is attached to a person or object to be tracked. A rotating set of blinders varies the view angle of a receiver disposed on a base unit. The receiver detects when the peak received signal occurs and uses that data to determine the angle between the aiming axis of the base unit and a line from the base unit to the transmitter. A servomechanism pans and tilts the base unit so as to decrease the angle to zero, thereby pointing the base unit's aiming axis at the transmitter.